Was lobster.rs ways invite only? I thought I remembered having an account a long time ago...but my email isn't registered when I go to reset my PW. Because it's a much smaller community it does suffer from low comment counts on posts. Comments are the best part of HN.
Invite only to write, open to read. But the main trick is tracking the invite tree - if the person that invited you gets banned, you get banned too (or need to appeal to have your “branch” of the invite tree adopted by someone else).